Apparatus for shock-forming of workpieces

ABSTRACT

Wall means surrounds a pressure chamber arranged to accommodate a workpiece and a die having a surface contour into conformance of which the workpiece is to be deformed by shock action. The wall means includes at least two walls at least one of which is movable relative to the other between a chamber-closing and a chamber-opening position, and the wall means has an inertia so selected as to at least substantially equal the necessary shockpressure for producing the predetermined energy level required to obtain the desired workpiece deformation so that, when the shockpressure is exceeded, relative movement of the walls to said chamber-opening position occurs with concomitant venting of the chamber. Shock-pressure producing means is provided and is activated for producing a sudden increase in pressure in the chamber. A recess has first and second openings communicating with the interior and exterior of the chamber, respectively, and accommodating the shock-pressure producing means. Inertial closure means serves to close the second opening which communicates with the exterior of the chamber.

United States Patent Hertel et al. 1 Feb. 15, 1972 [54] APPARATUS FOR SHOCK-FORMING Primary Examiner-Richard .I. l-lerbst OF WORKPIECES Attorney-Michael S. Striker [72] Inventors: Heinrich l-lertel; Dietrich Ruppln, both of 57 ABSTRACT Berlin, Germany Wall means surrounds a pressure chamber arranged to accom- [73] Asslgnee: Hemnch end, Beth", Germany modate a workpiece and a die having a surface contour into [22] Filed: Sept. 24, 1969 conformance of which the workpiece is to be deformed by shock action. The wall means includes at least two walls at PP 860,705 least one of which is movable relative to the other between a O chamber-closing and a chamber-opening position, and the [3 1 Foreign Apphcatlon Pnomy Data wall means has an inertia so selected as to at least substantially 7 equal the necessary shock-pressure for producing the Sept. 5, 1968 Germany ..P I7 77 210.0 predetermined energy level required to obtain the desired 52] US. Cl ..72/56 workpiece deformation so that, when the shook-Pressure is 51 m Cl B21 2 /03 ceeded, relative movement of the walls to said chamber-open- [58] Field of Search ..72/56; 29/421 E ing position occurs with concomitant venting of the chamber- Shock-pressure producing means is provided and is activated 56] Referen e Ci d for producing a sudden increase in pressure in the chamber. A recess has first and second openings communicating with the UNITED STATES PATENTS interior and exterior of the chamber, respectively, and accom- 2,93s,03s 5/1960 Chatten ..72/56 mating the Pmducmg 'F l 3 036 373 5/1962 Drexelius 72/56 sure means serves to close the second openmg which commu- 3045339 7/1962 C a ahan "72/56 nicates with the exterior of the chamber. 3,267,7i0 8/1966 lnoue ..72/56 13 Claims 4') F- 3,273,365 9/1966 Felts ..72/56 m 3 guns 3,338,080 8/ l967 Golden ..72/56 PATENTEDEEB 15 m2 3341.796

sum 2 OF 3 INVENTORS "Emma! HERTEL BY ZDIETQI an Run-Pm PATENTED FEB 1 5 I972 SHEET 3 (IF 3 INVENTOR HEINRICH HERTEI. BY DIET'QIcH RVPP'N Mow! dab-W APPARATUS FOR SHOCK-FORMING OF WORKPIECES BACKGROUND OF THE INVENTION The present invention relates generally to apparatus for shock-forming of workpieces, and more particularly to apparatus of this type which has a self-venting chamber.

It is known to deform workpieces to desired configuration by subjecting them to shock, that is by setting off explosives or analogous means in a confined space. It is also known to utilize self-venting pressure chambers in such apparatus, meaning pressure chambers with one or more walls moved to a position in which the pressure chamber is opened when the pressure in the chamber reaches and exceeds a predetermined level.

The means for maintaining the removable wall or walls in closed position against the developing pressure--until the pressure reaches the predetermined level at which the chamber is to open--usually requires significant structural and technological expenditures because of the forces which must be restrained. An attempt to simplify such devices is described in Gennan Pat. No. 1,259,825 which teaches a device wherein the pressure chamber is bounded by stationary and movable walls, with the mass of the movable walls being so selected that the developing pressure in the interior of the pressure chamber is largely counteracted--until it reaches the predetermined level at which venting is desired--by the inertia of the masses. This is a significant improvement over the constructions known from the prior art.

In all of these devices, including the last-mentioned one, the shock-pressure producing means utilizes a gunpowder charge and means for setting the charge off. Evidently, the charge itself and the means for setting it off must be supported in suitable fashion, and this is usually accomplished by providing a recess in one of the walls bounding the pressure chamber, and having the components in question located therein. However, the material defining this recess is subjected to high stresses when the charge is triggered, Because the interior of the recess must communicate not only with the interior of the chamber when the latter is closed, but because there must also be access available from the exterior in order to permit servicing of the shock-pressure producing means, for instance installation of the new charge, closure means is provided at the side of the recess which communicates with the exterior of the pressure chamber. Such closure means in known constructions may be of various different types, including screw closures and the like. This has been found to be less than satisfactory, however, because of the stresses-which are much greater than for the instance those exerted upon the barrel of a projectile weapon- -are so high that the known types of closure means provide safety hazards.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome these disadvantages.

A more particular object of the invention is to provide an improved device of the type under discussion.

Still more specifically an object of the invention is to provide an improved shock-forming apparatus having closure means for the recess accommodating the shock-closure producing means, which closure means is not possessed of the aforementioned disadvantages.

Still more specifically, it is an object of the present invention to provide such closure means which is of the inertial type.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides in an apparatus for shock-forming of workpieces, which comprises wall means surrounding a pressure chamber arranged to accommodate a workpiece and a die having a surface contour which is to be imparted to the workpiece by shock-deformation of the latter into conformance with the surface contour. The wall means includes at least two walls, at least one of which is movable relative to the other between a chamber-closing and a chamber-opening position, and the wall means has an inertia so selected as to at least substantially equal the necessary shock-pressure for producing the predetermined energy level requisite to obtain the desired deformation of the workpiece so that upon feeding of the necessary shock-pressure relative movement of the walls to the chamber-opening position results with concomitant venting of the chamber.

Shock-pressure producing means is activatable for producing a sudden increase in pressure in the chamber, and a recess is provided having first and second openings communicating with the interior and the exterior of the chamber, respectively, this recess accommodating the shock-pressure producing means. In accordance with the present invention, the second opening which communicates with the exterior of the chamber is closed by inertial closure means.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic axial section through an apparatus illustrating one embodiment of the invention;

FIG. 2 is a view similar to FIG. 1 but illustrating a further embodiment of the invention;

FIG. 3 is a view similar to FIG. 2, illustrating yet another embodiment of the invention; and

FIG. 4 is a view similar to FIG. 3 and illustrating still a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing firstly the embodiment illustrated in FIG. 1, it will be seen that reference numeral 1 identifies a pressure chamber surrounded by a circumferential wall, a top wall 3 and a bottom wall 6 which at the same time constitutes the die and is provided with a surface contour 7 into conformance with which the workpiece 8 is to be deformed by development of shock-pressure in the interior of the chamber 1.

Reference numeral 5 is a support for the combined wall and die 6.

Reference numeral 3 is a closure plate arranged intermediate the circumferential wall 2 and the top wall 4. A support plate 9 is provided and rigidly connected therewith are yoke members 10, and the various elements surrounding and defining in their interior the pressure chamber 1 are connected with one another via the plate 9 and the yoke members 10, and further via the elastically yieldable members 11, which may be spring members such as rubber springs, and which are fixed by guide bolts 12. They thus make possible the relative movement of the elements 3 and 4 on the one hand and 5 and 6 on the other hand which it is necessary for obtaining the inertial closure and subsequent venting of the pressure chamber 1.

The circumferential wall 2 is provided with a beveled edge portion 13 which assures that during operation of the device, it is when the shock-pressure builds up in the interior of the chamber 1, the wall 2 will remain in precisely defined abutment with the elements 5 and 6 which avoids undesired movements of the wall 2 which could cause tilting.

Mounted in the plate 3 is a charge support 14 received in a recess 3a one end of which communicates with the interior of the chamber 1 and the other end of which communicates with the exterior of the chamber 1. In the illustrated embodiment the shock-pressure producing means is a cartridge 15 provided with suitable gunpowder which is to be triggered. The support 14 may be rigid with the plate 3 or, to facilitate the changing of the charge when the same has been triggered, it may be accommodated removably in the recess 3a provided in the plate 3. Reference numeral 16 diagrammatically illustrates means for triggering the charge 15 and when this takes place, the explosive force of the charge is transmitted through the pressure transmitting medium accommodated in the interior of the pressure chamber 1--and illustrated but not separately identified with a reference numeral--to the workpiece 8 to thereby deform the same into conformance with the surface contour 7. The space which is initially included between the surface contour 7 and the workpiece 8--as shown in FIG. 1-- may be evacuated via an evacuating conduit 17 which communicates with the space and in known manner communicates with a suitable source of suction which is not illustrated--if the space is sealed, for instance by providing a seal 18 in form of anO-ring or the like, if desired in connection with a sealing foil 19.

The rapidly building pressure in the interior of the chamber 1 on the one hand accelerates the workpiece 8 in the desired manner, by deforming it into conformance with the surface contour 7, and on the other hand it acts upon the underside of the plate 3 and accelerates this in the direction towards the blade 4. The inertial force of the plate 4, which is accelerated together with the plate 3 because of its connection with the same, serves to affix the support 14 and the cartridge 15 in their requisite position and to prevent them form being ejected from the recess.

Once the pressure in the interior of the chamber 1 exceeds a predetermined level, required for obtaining the desired deformation of the workpiece 8, it overcomes the inertia of the wall 3, whereby the wall 3 moves away from abutment with the wall 2 and venting occurs. The yoke members are connected with the plate 4 via the slides 20 so as to be releasable to thereby facilitate separation of individual components from one another. The slide connection 20 is so constructed that the triggering means 16 is in position to trigger the charge only when the walls 2 and 3 are in abutment defining the pressure chamber in its closed condition. This is a safety factor in the operation of the device.

The elements 1-20 of the apparatus illustrated in FIG. 1 define with one another a complete system which is closed in itself, meaning that when the charge is triggered no reaction forces are allowed to escape to the exterior because they are absorbed by the inertial forces which the shock-pressure must overcome as well as by the presence of the spring element 11. The device may be accommodated loosely in a protective enclosure 21 which preferably serves to restrain and collect the pressure transmitting medium which is ejected from the interior of the chamber 1 when venting thereof occurs.

The embodiment illustrated in FIG. 2 differs from that in FIG. 1, as is evident. The embodiment in FIG. 2 is particularly suitable for larger constructions. Again, the pressure chamber is identified with reference numeral 1. It is defined by the upper movable mass 22 and the lower movable mass 23 which serves to support the die. The charge support 24 with the charge 15 is located above the upper movable mass 24 exteriorly of the chamber 1 and is connected with the latter through the bore 25. The cover plate 4 is guided by the guide rods 26 in such a manner that relative movement is possible between the upper mass 22, the support 24 and the plate 4'. The latter carries the diagrammatically illustrated triggering device 27 which may be actuated in known manner hydraulically, mechanically, pneumatically or electrically. Regardless of how the activation is effected, when the charge 15 is ignited the pressure is transmitted to the bore 25 into the pressure transmitting medium in the interior of the chamber 1. The deformation of the workpiece 8 then occurs as before into conformance with the surface contour of the die 6.

It is evident that the upper movable mass 22 is accelerated by the buildup of pressure in the interior of the chamber 1, in direction towards the plate 4', and that the support 24 arranged between the components 22 and 4' is retained and closed, together with the charge 15, because of the developing inertial forces. The elements 4, 15, 22, 24, and 26 move along the guide rods 28, guided in the sleeves 29, in upward direction until the initial energy transmitted to them corresponds to the achieved potential energy in the gravitational field. At the same time, the lower movable mass 23 moves in opposite direction, that is in downward direction, and its initial energy is absorbed by spring elements 30. The oppositely directed movements of the upper movable mass and the lower movable mass 23 open the chamber 1 and serve to vent the same.

Means may be provided, here illustrated as the hydraulically operating device 31, for retaining the connected elements 22, 15, 4, 26 and 27 in the region of the upper apex of their movement. In order to avoid peak stresses of the acceleration from acting upon the device 31, the connection between the same and the plate 4 may be elastic via the interposition of a spring element 32. When the upper movable movements have been prevented from further movement by the device 31, the upper movable mass 22 descends because of its inherent weight by the distance which is permitted by the guide rods 26. This then again permits axis to the charge support 24 so that the latter can be provided with a new charge.

Shock absorbers 33 serve to dampen the oscillations which occur by transmittal of force to the springs which support the lower movable mass 23. The outer cover or enclosure 34 surrounds the device and serves to retain and collect a pressuretransmitting medium which is ejected from the chamber 1 when the latter is vented. At the same time, it serves to dampen the noise transmitted. Openings 35 in the enclosure 34 permit access to the apparatus within it. The guide rods 28, together with the plate 36 and the cross member 37 form the supporting frame of the device.

The embodiment illustrated in FIG. 3 shows the charge support 14' to be arranged in the interior of the pressure chamber 1 which is defined between the upper movable mass 22 and the lower movable mass 23. The construction and arrangement of the device in FIG. 3 corresponds substantially to that of FIG. 2, except for the construction and arrangement of the charge support 14.

With reference to the latter it is pointed out that the closure of the charge support 14 occurs as, after the cartridge or charge is ignited, the lower mass 23 together with the die 6 is accelerated downwardly, whereas the upper mass 22' together with the charge support 14' is accelerated upwardly. By suitably dimensioning the surfaces of the upper mass 22 and the charge support 14', as well as similarly dimensioning the masses of these elements, it is assured that the charge support 14 receives from the internal pressure in the chamber 1 a higher acceleration than the upper movable mass 22'. The inertial forces resulting from this differential in the acceleration of the charge support 14 versus that of the upper movable mass 22' serve to inertially close during the acceleration phase of the movement the charge support 14' in the manner according to the present invention.

An auxiliary device, for instance a double acting hydraulic cylinder 36, can serve to downwardly remove the charge support 14' after the device has been triggered, in order to facilitate ready insertion of a new charge. The device 31' is again provided as discussed in conjunction with FIG. 2. When the charge support 14' is removed for recharging, it can be tilted if necessary about the support 38 out of the interior of the upper movable mass 22'.

Coming, finally, to the embodiment illustrated in FIG 4 it will be seen that here the charge support 14" is again arranged in the interior of the upper mass 22, as in the embodiment of FIG. 3. The lower movable mass 23 is guided on the short guide rods 28' and moves with the aid of the elements 30 and 33, being springily supported and damped by the same, in downward direction in the same manner as discussed with reference to FIGS. 2 and 3.

During its upward movement after triggering of the charge the upper movable mass 22' is guided by the guide rods 28". The latter are mounted in the cross member 37' of the machine frame with the spring elements 39 and the abutments 40 in such a manner that they are capable of performing a short vertical sliding movement.

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In the embodiment of FIG. 4 the charge support 14" is so secured to the lower end of the guide rods 28" that the upper movable mass 22 rests on the charge support 14" when the chamber 1 is closed. The vertical sliding capability of the guide rods 28 assures the tight abutment of the charge support 14'' against the upper movable mass 22' with simultaneous abutment of the upper movable mass 22 against the lower movable mass 23.

When the charge is triggered, the upper movable mass 22' moves upwardly as discussed with respect to FIGS. 2 and 3, and is detained by the device 31 as discussed earlier. The charge support 14'', whose mass and whose surface exposed to the explosive force must be so selected as discussed with respect to FIG. 3, that is so that the force acting upon the surface of the charge support 14" is greater than that acting upon the exposed surface in the exterior of the chamber 1 of the upper movable mass 22, is first pressed against the upper movable mass 22 when the charge is triggered, before the two move upwardly together. This provides the desired closing of the support against ejection of the charge.

Because relative to the pressure-developing time in the interior of the chamber 1 the upper movable mass 22 moves only slowly, the short distance by which the guide rods 28" are slidable, is sufficient to maintain the closure of the charge support during the pressure development time.

Once the guide rods 28" abut against the abutments 40, the charge support 14" remains stationary whereas the upper movable mass 22' continues to move upwardly to the apex of its movement.

Contrary to the embodiments in FIGS. 2 and 3, the guide rods 28 and 28" in the device illustrated in FIG. 4 cannot serve as a supporting frame for the apparatus. The latter must therefore be provided with a supporting frame 34 which at the same time may be constructed to retain and collect pressure-transmitting medium which is ejected during venting of the chamber 1, and which may also be constructed to dampen the sounds resulting from triggering of the charge.

It will be appreciated that the apparatus which has been described by way of the exemplary embodiment in FIGS. 1-4 presents a significant and advantageous advancement over what is known currently in the art. Not only do they provide for reliable closure of the charge support under all circumstances, but also this closure is simple to construct, provides for automatic unclosing without mechanical devices necessary to correct this, and provides for very good material strength characteristics because the strength of the material need not be weakened by cutting threads or analogous means into it which could be subject to material fatigue under the repeated stresses resulting from repeated use of the device.

The embodiment illustrated in FIG. 1 is particularly suitable for small apparatuses because it is so simple and easy to operate. The embodiments in FIGS. 2-4 are particularly suitable for larger dimensioned apparatuses. They are simple in their construction but permit mechanizing or automating of the charge and operating phases so that short operating periods can be readily attained with these constructions. The relative movement between charge support and closure plate or the upper movable mass which occurs in the embodiments in FIGS. 2-4 when the charge support automatically opens, may be used in known manner for ejecting a cartridge casing if one is present. In the embodiment of FIG. 3 the cartridge casing may be injected with an auxiliary device 36.

When the charge support is arranged according to FIGS. 3 and 4 it remains accessible from the loading plane even when the device is made large. This is necessary both where the device is to be manually charged and if the device is to be modified so that charging occurs by automation because it eliminates difficulties in gaining access for repairs and maintenance.

It is evident that in the embodiments of FIGS. 1, 2 and 4 the cartridge can be triggered only when the chamber is closed because only then will the triggering arrangement come in contact with the charge. In the embodiment of FIG. 3 this safety arrangement can be achieved by so constructing the device that the upper movable mass 22 and the charge support must move relative to one another in such a manner that the charge support moves to its end position only after the chamber 1 is closed. Evidently, in all four embodiments this is a significant improvement in the safety of operation.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in an apparatus for shock-forming of workpieces, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. Apparatus for shock-forming of workpieces, comprising wall means surrounding a pressure chamber arranged to accommodate a workpiece and a die having a surface contour which is to be imparted to said workpiece by shock deformation of the latter into conformance with said surface contour, said wall means including at least two walls at least one of which is movable relative to the other between a chamberclosing and a chamber-opening position, and said wall means having a first inertia so selected as to at least substantially equal the necessary shock-pressure for producing the predetermined energy level requisite to obtain the desired deformation of said workpiece so that upon exceeding of said necessary shock-pressure relative movement of said walls to said chamber-opening position results with concomitant venting of said chamber; shock-pressure producing means activatable for producing a sudden increase in pressure in said chamber; a recess having first and second openings communicating with the interior and exterior of said chamber, respectively, and accommodating said shock-pressure producing means; and inertial closure means for closing said second opening which communicates with the exterior of said chamber, and having a second inertia so selected as to withstand said shock-pressure in said chamber.

2. Apparatus as defined in claim 1, said recess being provided in one of said walls, and said shock-pressure producing means being a gunpowder charge; and wherein said inertial closure means comprising a closure member overlying said second opening exteriorly of said chamber and having a mass so selected that it has said second inertia.

3. Apparatus as defined in claim 2; and elastically yieldable means connecting said walls to one another and connecting said closure member to said walls.

4. Apparatus as defined in claim 1; further comprising a wall element located exteriorly of said chamber and provided with said recess, and conduit means connecting said first opening with the interior of said chamber.

5. Apparatus as defined in claim 1; and further comprising retaining means retaining said walls and said inertial closure means against movement in excess of a predetermined distance in response to activation of said shock-pressure producing means and concomitant production of said shockpressure.

6. Apparatus as defined in claim 1, said recess being provided in one of said walls, and said inertial closure means including a closure member overlying said second end of said recess exteriorly of said one wall; and elastically deformable means interposed between said one wall and said closure member. v

7. Apparatus as defined in claim 1, at least one of said walls being movable relative to the other; and further comprising a wall element provided with said recess and so mounted in said chamber as to be in contact with said one wall when said shock-pressure producing means is activated.

8. Apparatus as defined in claim 7, the relative masses and exposed surface areas of said wall element and said one wall being so selected that an activation of said shock-pressure producing means said wall element is subjected to greater acceleration than said one wall, the resulting pressure differential effecting closing of said second end.

9. Apparatus as defined in claim I; further comprising a wall element provided with said recess; and moving means for moving said wall element with reference to said wall means.

10. Apparatus as defined in claim 1; further comprising a wall element provided with said recess; and mounting means mounting said wail element for pivotal movement relative to said wall means between an operative position and an inoperative position.

11. Apparatus as defined in claim 2; and guide means slidably connecting said wall element with one of said walls,

and said one wall with the other of said walls.

12. Apparatus as defined in claim 11, said shock-pressure producing means being a gunpowder cartridge, and further comprising detonating means for detonatin g the gunpowder in said cartridge, and activator means for activating said detonating means; and wherein said guide means is operative for maintaining said activator means remote from said detonating means when said walls are in chamber-opening position.

13. Apparatus as defined in claim 1, one of said walls being an upper wall and one of said walls being a lower wall below said upper wall; and elastic support means elastically supporting said lower wall. 

1. Apparatus for shock-forming of workpieces, comprising wall means surrounding a pressure chamber arranged to accommodate a workpiece and a die having a surface contour which is to be imparted to said workpiece by shock deformation of the latter into conformance with said surface contour, said wall means including at least two walls at least one of which is movable relative to the other between a chamber-closing and a chamberopening position, and said wall means haviNg a first inertia so selected as to at least substantially equal the necessary shockpressure for producing the predetermined energy level requisite to obtain the desired deformation of said workpiece so that upon exceeding of said necessary shock-pressure relative movement of said walls to said chamber-opening position results with concomitant venting of said chamber; shock-pressure producing means activatable for producing a sudden increase in pressure in said chamber; a recess having first and second openings communicating with the interior and exterior of said chamber, respectively, and accommodating said shock-pressure producing means; and inertial closure means for closing said second opening which communicates with the exterior of said chamber, and having a second inertia so selected as to withstand said shock-pressure in said chamber.
 2. Apparatus as defined in claim 1, said recess being provided in one of said walls, and said shock-pressure producing means being a gunpowder charge; and wherein said inertial closure means comprising a closure member overlying said second opening exteriorly of said chamber and having a mass so selected that it has said second inertia.
 3. Apparatus as defined in claim 2; and elastically yieldable means connecting said walls to one another and connecting said closure member to said walls.
 4. Apparatus as defined in claim 1; further comprising a wall element located exteriorly of said chamber and provided with said recess, and conduit means connecting said first opening with the interior of said chamber.
 5. Apparatus as defined in claim 1; and further comprising retaining means retaining said walls and said inertial closure means against movement in excess of a predetermined distance in response to activation of said shock-pressure producing means and concomitant production of said shock-pressure.
 6. Apparatus as defined in claim 1, said recess being provided in one of said walls, and said inertial closure means including a closure member overlying said second end of said recess exteriorly of said one wall; and elastically deformable means interposed between said one wall and said closure member.
 7. Apparatus as defined in claim 1, at least one of said walls being movable relative to the other; and further comprising a wall element provided with said recess and so mounted in said chamber as to be in contact with said one wall when said shock-pressure producing means is activated.
 8. Apparatus as defined in claim 7, the relative masses and exposed surface areas of said wall element and said one wall being so selected that an activation of said shock-pressure producing means said wall element is subjected to greater acceleration than said one wall, the resulting pressure differential effecting closing of said second end.
 9. Apparatus as defined in claim 1; further comprising a wall element provided with said recess; and moving means for moving said wall element with reference to said wall means.
 10. Apparatus as defined in claim 1; further comprising a wall element provided with said recess; and mounting means mounting said wall element for pivotal movement relative to said wall means between an operative position and an inoperative position.
 11. Apparatus as defined in claim 2; and guide means slidably connecting said wall element with one of said walls, and said one wall with the other of said walls.
 12. Apparatus as defined in claim 11, said shock-pressure producing means being a gunpowder cartridge, and further comprising detonating means for detonating the gunpowder in said cartridge, and activator means for activating said detonating means; and wherein said guide means is operative for maintaining said activator means remote from said detonating means when said walls are in chamber-opening position.
 13. Apparatus as defined in claim 1, one of said walls being an upper wall and one of said walls being a lower wall below said upper wall; and elastic support means elastically supPorting said lower wall. 